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Entanglement activation from quantum coherence and superposition
摘要： Quantum entanglement and coherence are two fundamental features of nature, arising from the superposition principle of quantum mechanics. While considered as puzzling phenomena in the early days of quantum theory, it is only very recently that entanglement and coherence have been recognized as resources for the emerging quantum technologies, including quantum metrology, quantum communication, and quantum computing. In this work we study the limitations for the interconversion between coherence and entanglement. We prove a fundamental no-go theorem, stating that a general resource theory of superposition does not allow for entanglement activation. By constructing a quantum controlled-NOT gate as a free operation, we experimentally show that such activation is possible within the more constrained framework of quantum coherence. By using recent results from coherence theory, we further show that the trace norm entanglement is not a strong entanglement monotone.
关键词： quantum technologies,entanglement activation,quantum entanglement,quantum coherence,trace norm entanglement,no-go theorem,superposition principle
更新于2025-09-09 09:28:46
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Proving genuine multiparticle entanglement from separable nearest-neighbor marginals
摘要： We address the question of whether or not global entanglement of a quantum state can be inferred from local properties. Specifically, we are interested in genuinely multiparticle entangled states whose two-body marginals are all separable, but where the entanglement can be proven using knowledge of a subset of the marginals only. Using an iteration of semidefinite programs we prove that for any possible marginal configuration up to six particles multiqubit states with the desired properties can be found. We then present a method to construct states with the same properties for more particles in higher dimensions.
关键词： quantum entanglement,marginal problem,semidefinite programming,multiparticle entanglement
更新于2025-09-09 09:28:46
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Concatenation of Keys in Quantum Cryptography: How Quantum Entanglement “Penetrates to” Classical Devices
摘要： Quantum mechanics admits collective measurements that are related to the projection onto entangled states and allow one to retrieve more classical information from an ensemble of quantum states compared with individual measurements. In this relation, a fundamental question arises for key secrecy in quantum cryptography. Should the secrecy criterion be formulated with regard to all keys distributed both on previous and future quantum key distribution (QKD) sessions, or it suffices to guarantee key secrecy only in an individual QKD session? The study of this question is the subject of the present paper.
关键词： quantum entanglement,quantum key distribution,quantum cryptography,secrecy criterion,collective measurements
更新于2025-09-09 09:28:46
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Negative-temperature-state relaxation and reservoir-assisted quantum entanglement in double-spin-domain systems
摘要： Spin collective phenomena including superradiance are even today being intensively investigated with experimental tests performed based on state-of-the-art quantum technologies. Such attempts are not only for the simple experimental verification of predictions from the last century, but also as a motivation to explore new applications of spin collective phenomena and the coherent control of the coupling between spin ensembles and reservoirs. In this paper, we investigate the open quantum dynamics of two spin ensembles (double-spin domains) coupled to a common bosonic reservoir. We analyze in detail the dynamics of our collective state and its structure by focusing on both the symmetry and asymmetry of this coupled spin system. We find that when the spin size of one of the double domains is larger than that of the other domain, at the steady state this system exhibits two unusual collective behaviors: the negative-temperature-state relaxation in the smaller spin domain and the reservoir-assisted quantum entanglement between the two domains. These results are the consequence of the asymmetry of this system and the decoherence driven by the common reservoir.
关键词： negative-temperature-state relaxation,spin collective phenomena,bosonic reservoir,superradiance,quantum entanglement,quantum dynamics
更新于2025-09-09 09:28:46
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Quantum secure ghost imaging
摘要： In this work, we propose a scheme of quantum secure ghost imaging (QSGI), which combines temporal quantum ghost imaging and security test based on quantum entanglement. Utilizing the quantum feature of entangled photon pairs, the eavesdropping in the imaging process can be detected, with a certain degree of protection on the object information. The proposed scheme is demonstrated by experiment, in which photon pairs are generated by a quantum light source based on a silicon waveguide. Two-dimensional patterns are imaged line by line over 50 km optical fibers and the security test is realized by two-photon interference for energy-time entanglement. QSGI could be applied in scenarios of secure imaging and surveillance, and may inspire new ideas on specific quantum communication tasks.
关键词： quantum entanglement,quantum secure ghost imaging,secure imaging,quantum communication
更新于2025-09-04 15:30:14
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Entanglement of single-photons and chiral phonons in atomically thin WSe2
摘要： Quantum entanglement is a fundamental phenomenon that, on the one hand, reveals deep connections between quantum mechanics, gravity and spacetime1,2, and on the other hand, has practical applications as a key resource in quantum information processing3. Although it is routinely achieved in photon–atom ensembles4, entanglement involving solid-state5–7 or macroscopic objects8 remains challenging albeit promising for both fundamental physics and technological applications. Here, we report entanglement between collective, chiral vibrations in a two-dimensional WSe2 host—chiral phonons (CPs)—and single-photons emitted from quantum dots9–13 (QDs) present in it. CPs that carry angular momentum were recently observed in WSe2 and are a distinguishing feature of the underlying honeycomb lattice14,15. The entanglement results from a ‘which-way’ scattering process, involving an optical excitation in a QD and doubly-degenerate CPs, which takes place via two indistinguishable paths. Our unveiling of entanglement involving a macroscopic, collective excitation together with strong interactions between CPs and QDs in two-dimensional materials opens up ways for phonon-driven entanglement of QDs and engineering chiral or non-reciprocal interactions at the single-photon level.
关键词： chiral phonons,WSe2,two-dimensional materials,quantum dots,Quantum entanglement
更新于2025-09-04 15:30:14